1. Field of the Invention
This invention relates to a method for the application of a refractory spray material to various ceramic furnace walls.
2. Description of the Prior Art
In recent years, the spraying method for application of a refractory material is following the direction of finding growing utility owing to the advantages (1) that the operation is simple because the spraying work can be performed without the need to use a frame for application, (2) that the massive application of a spray material can be attained within a short period of time, (3) that the apparatus can be assembled and repaired with great ease, and (4) that the spraying can be perfomed hot or cold at needs, coupled with the improvements achieved in spraying machines and nozzles.
This spraying method, meanwhile, suffers from the disadvantages (1) that the rebound loss generally runs on the order of 20% and often rises past 30% under certain conditions, so that a material loss is far greater than that involved in the casting method, (2) that the spraying entails the formation of dust in the environment of work, (3) that the adhesiveness of the applied material is not enhanced unless a larger amount of a binder is used than that in the casting method, and (4) that the refractoriness of the refractory material applied by the spraying method is liable to become lower than that of the material applied by the casting method, when aggregate of the same grade is used.
As a solution of these disadvantages, a method is now in vogue which comprises adding powdery sodium silicate as a binder to the spray material and admixing the spray material with water just before the spray material reaches the spray nozzle.
Even after the powdery sodium silicate is mixed with water, it does not exhibit its effect as a binder unless it is completely dissolved in water. However, the mixture ejected through the spray nozzle reaches the substrate in one second or shorter, so that the complete dissolution of sodium silicate in the accompanying water can never be expected during the short span of time.
The major part of the powdery sodium silicate, after having reached the substrate, gradually dissolves and begins to exhibit its effect as a binder. The powdery sodium silicate is consequently consumed in a manner such that its effect is not sufficiently exhibited. To overcome the difficulty, there has been generally practised a method which comprises premixing an excess amount of powdery sodium silicate in the spray material to make up for the insufficient result aforementioned.
The incorporation of the powdery sodium silicate in such an excess amount as aforementioned results in serious deterioration of the refractoriness of the spray material. As a result, even when the spray material mixed with the powdery sodium silicate as a binder may be used, it is difficult to enhance a ratio of adhesion above 85%.
For the improvement of these conventional methods, spraying methods using various binder solutions have been proposed in the specification of Japanese Patent Application Laid-open No. 55-000816, the specification of Japanese Patent Application Laid-open No. 55-015948, etc. Even in these proposed methods, since no sufficient affinity is obtained between the spray material and the binder solutions, it is difficult to obtain a ratio of adhesion exceeding 85% at all times. Some of the binders proposed so far are of such a nature that the preparation of their aqueous solutions itself induces the hydrolysis of the binders, so that the aqueous solutions prepared in this way have the inherent effects of binders reduced or completely lost.
As the means of completely damping the spray powder itself, the use of an amorphous refractory material in the form of slurry containing a curing agent has been proposed in the specification of Japanese Patent Publication No. 57-007350. In order to smoothly pneumatically convey the amorphous refractory material in the slurry form, the refractory material shall have proper softness. As a result, this material applied onto a predetermined substrate is liable to involve the phenomenon of weeping. Besides, the amount of a curing accelerator to be mixed in the spray material inside the nozzle is very small in general, so that the accelerator is not sufficiently dispersed in the spray material. The method, therefore, has the disadvantage that it is difficult to obtain a uniformly spray-coated body. Besides, the pretreatment for forming the amorphous refractory material (castable) containing a curing agent into the slurry inevitably imposes a limit upon the length of time during which the material is effectively usable. Consequently, the method has the disadvantage that the use of this material induces the phenomenon of clogging in the hose for pneumatic conveyance.